If several tracks of a filter or various tracks of different filters are positioned on a piezoelectric substrate in close proximity to each other, capacitive interaction may arise between the metal plating that forms component structures such as transducers and bus bars, and especially between bus bars positioned perpendicular to the track of two different acoustic tracks. If two acoustic tracks are interconnected and are associated with the same filter, this normally causes the stop-band selection to change. If electromagnetic coupling arises between the acoustic tracks of two independent filters, then this can lead to deterioration in insulation. The effect of this is that unwanted or foreign signal fragments are received by the input of one or the other filter, which affects the actual signal and, therefore, should be avoided. In general, such capacitive interaction is referred to as crosstalk.
If DMS filters are used, the traducers can be positioned in several interconnected tracks. Normally, the acoustic tracks are arranged in parallel for this purpose, and are in close proximity to each other in order to save costly chip surface area. The arrangement may include transducers that are opposite each other and/or bus bars of different tracks in close proximity
With input and output transducers, for example, this can lead to significant crosstalk which degrades the filter's selection. This problem arises frequently when the bus bar of the input or output transducer facing a neighboring track is connected to a voltage that is different from ground. Particularly pronounced effects also occur with transducers where the electrical connection of the transducer takes place from one side of the acoustic track, on which the corresponding bus bar is then divided into two sub-bars which are connected to the two terminals. The bus bar located opposite is one piece and is not connected to an externally applied voltage, and therefore assumes a floating voltage (intermediate voltage). If such a transducer, e.g., known from DE 100 13 861 A1 and also known as a v-split transducer, is accessed symmetrically (balanced), then the floating bus bar represents a virtual ground. This means that for a symmetrical connection and otherwise optimized symmetrical design of the remaining filter, the floating voltage is exactly on ground. However, if the voltage of this virtual ground deviates from zero, then symmetry disruption exists, which leads to an impairment of the filter function and results in a lower stop-band selection. This type of “drifting” in the virtual ground of dual track or multiple track DMS filters of this kind may be caused by electromagnetic coupling.